Aeronautical and aerospace technicians design, construct, test, operate, and maintain the basic structures of aircraft and spacecraft, as well as propulsion and control systems. They work with scientists and engineers. Many aeronautical and aerospace technicians assist engineers in preparing equipment drawings, diagrams, blueprints, and scale models. They collect information, make computations, and perform laboratory tests. Their work may include working on various projects involving aerodynamics, structural design, flight-test evaluation, or propulsion problems. Other technicians estimate the cost of materials and labor required to manufacture the product, serve as manufacturers' field service technicians, and write technical materials. There are approximately 11,400 aerospace technicians and 137,300 aircraft and avionics equipment mechanics and service technicians employed in the United States.